Start Your Engines: Solid-State Magneto Start Booster

Nov. 1, 2002
The techniques and opinions on how to start aircraft engines are as varied as the airplanes, engines, and operators that encompass this topic.

Solid-State Magneto Start Booster

By Harry Fenton

The techniques and opinions on how to start aircraft engines are as varied as the airplanes, engines, and operators that encompass this topic. Starting problems can be caused by poor operator technique, cold weather, hot restarts, poor priming, or problems inherent with some engine designs (in that some are just harder to start than others). Whatever the reason, starting problems are time-consuming, frustrating, and costly.

Unison Industries, an ignition system manufacturer, has developed a device to specifically address the dilemma of hard starting aircraft engines. SlickSTART™ is a magneto starting booster which uses solid-state electronics with capacitive discharge technology to improve the performance of engines with poor starting characteristics.


SlickSTART improves aircraft engine starting by delivering 340 percent more spark energy to an aircraft’s spark plugs than conventional impulse coupled or retard breaker magneto systems. By increasing spark energy and the number of spark events each second, SlickSTART boosts the magneto’s electrical output to overcome hard starting issues caused by fouled spark plugs, poor priming, hot engine restarts, and extreme cold weather

conditions. Other direct benefits for the aircraft operator include reduced electrical stress on starter motors and batteries and improved dispatch capability of the aircraft under conditions likely to result in hard starting.


SlickSTART is STC-approved to be installed on airframes and engines equipped with most models of Slick and TCM/Bendix magnetos. SlickSTART P/N SS1001 is used with the Slick 4200/6200 and the latest model Slick 4300/6300 series magnetos, but is not approved for use with obsolete 4000/4100 or 400/600 series magnetos. SlickSTART P/N SS1002 is approved for all TCM/Bendix 20/200 and 1200 series magnetos, but is not approved for the Bendix D2000/D3000 dual magnetos series. For most aircraft equipped with an existing starting vibrator, the SlickSTART can be bolted right in place of existing equipment. For new installations, the SlickSTART can easily be mounted to the aircraft firewall. Both SlickSTART part numbers can be used with either 12- or 24-volt aircraft electrical systems.

As SlickSTART is designed to boost only one impulse coupled or retard breaker magneto, a second SlickSTART can be installed on engines configured with two impulse coupled or retard breaker magnetos. Some helicopter applications, notably the Schweizer 269 series, use two vibrators so two SlickSTARTs would be required to accomplish a complete retrofit.

How it works

SlickSTART is energized when the ignition switch is in the "start" position, and provides high electrical output only when needed – during engine start. SlickSTART stores electrical energy in a series of capacitors and increases the voltage prior to delivery to the magneto circuit. When triggered, the high energy capacitive voltage of the SlickSTART is discharged into the coil via the magneto primary circuit. When the contact points open, the electrical charge in the secondary field collapses and discharges through the distributor block circuit. The resulting capacitive/inductive spark arcs across the distributor electrode and distributor tower air gap with peak voltages as high as 23kV (depending upon the spark demand requirements at the spark plug).

At first glance, the SlickSTART may appear to be functionally similar to the TCM/Bendix vibrator, but aside from a couple of common wiring connections, the SlickSTART has little in common with electro-mechanical starting vibrators. The solid-state electronic components of SlickSTART are hermetically sealed, do not wear, and do not require cleaning or adjustment.

The vibrator cannot boost impulse coupled magnetos and does not appreciably improve the voltage output of retard breaker magnetos. Typical starting voltage for an impulse coupled magneto application is only around 17kV at 1 spark per second (sps) at top dead center (TDC). However, with SlickSTART augmenting the primary output of the impulse coupled magneto, the output of the magneto is increased to nearly 23kV at 14 sps and continues to be delivered as long as the contact points are open, up to 60 degrees beyond TDC. Similarly, the output of a vibrator type ignition runs about 11kV at 11 sps while the SlickSTART-boosted magneto can produce nearly 23kV at 14 sps, effectively doubling the voltage and increasing the sparks per second available during start.


The higher peak voltage and energy of the SlickSTART will initiate combustion of very lean or very rich mixtures and will fire plugs fouled by oil or fuel, whereas the same conditions may not be overcome by a standard impulse coupled or retard breaker magneto system. The longer duration of the SlickSTART spark event also allows more time for a combustible mixture to pass near the spark plug tip when a spark event occurs, further enhancing the SlickSTART’s capability to fire plugs during the most unforgiving of conditions.


Installation can be accomplished in about one hour and can be done with standard shop tools. Slick Service Letter SL2-96 provides complete installation documentation and includes the Supplemental Type Certificate. For certified aircraft, an FAA Form 337 will need to be completed after installation. Please note that the aircraft battery and ignition harness will need to be disconnected before installing SlickSTART and normal precautions must be taken when the P-lead is detached from the magneto, as accidental ignition is possible. Airframe manufacturer manuals may also be needed for additional wiring schematics.

There are several possible SlickSTART installations. The optimum mounting position is with the terminals facing down, on the engine side of the firewall. There are some applications, such as Mooney aircraft when an existing vibrator is being replaced, that require mounting in an inverted position with the terminals facing upward. The remaining installation procedures differ depending on the type of application.

When mounting on a firewall, locate a spot and drill two holes to match the bolt hole pattern. The unit is then attached with standard AN hardware. It may also be mounted on motor mount tubes, but there must be a ground path from the SlickSTART mounting base to airframe ground. If cushioned clamps are used, then a separate bonding strap must be installed from the base to airframe ground.

The simplest installation scenario is for impulse coupled magnetos. A wire connection from terminal 1 on the SlickSTART connects to the impulse coupled magneto’s capacitor terminal stud. Pin 2 and 3 are left unconnected in this installation. Voltage-In (VIN) is connected to the positive switched side of the starter solenoid. The ground terminal is connected to the ground point on the left magneto, or mag cover on Bendix magnetos.

Installation of SlickSTART and P-lead wires on magneto. Note how P-lead and SlickSTART boost wire are piggybacked and share the same terminal.

To install a SlickSTART as a replacement unit for the Bendix "Shower of Sparks" vibrator, first determine if the vibrator is a relay or non-relay type. A vibrator with a relay switches between primary and retard points while grounding the right magneto to prevent against kickback during engine start. The ignition switch controls these functions in a non-relay vibrator application. SlickSTART can be used with either application, but must be wired according to the specific installation instructions and wiring schemes detailed in Service Letter SL2-96.

Since the existing bolt hole pattern matches SlickSTART’s pattern, new holes will not have to be drilled and the SlickSTART can simply be bolted in place of the existing vibrator. Please note that this remove and replace installation does not apply to twin engine aircraft using a single vibrator. There is a subtle circuit difference between SlickSTART and vibrators. On twin engine applications using a single vibrator, SlickSTART will run continuously, so an individual SlickSTART is required for each engine.

Terminal 1, VIN, and ground terminals are all connected in this same manner. Terminal 2 connects to the right magneto capacitor terminal stud and terminal 3 connects to the magneto retard breaker terminal. To install a SlickSTART as a replacement for the Bendix "Shower of Sparks" vibrator that does not include a relay, the instructions are the same, except terminal 2 is left unconnected.


Once SlickSTART is installed, there is little maintenance required. However, the L-1492 SlickSTART installation, operation, maintenance, and troubleshooting manual does provide some continuing maintenance information. At 500 hours, inspect all wires and terminals for corrosion, contamination, arcing, and proper alignment. Also check the security of the mounting. Cleaning may be done using a mild detergent and water solution and dried with a soft cloth. Operation of the SlickSTART can be confirmed by removing the top spark plugs from the engine, disconnecting the power lead to the starter, and then engaging the ignition switch in the start position. As an assistant rotates the engine crankshaft to the TDC position, the impulse coupling or retard breaker points should trigger. The boosted spark generated by the SlickSTART will be clearly obvious at the spark plugs. The sparks will be bright white and continuous if the crankshaft is dwelled at the point where the magneto fires.

SlickSTART is a completely sealed solid-state device that requires no internal maintenance. In fact, should the unit be opened, it is not considered airworthy, as it no longer conforms to FAA approval.

Wiring connections at SlickSTART for impulse coupled magneto installation.


No changes are necessary to the current Pilot Operating Handbook, as SlickSTART is only activated when the ignition switch is in the "start" position. To start the engine, follow the procedures detailed in the Pilot’s Operating Handbook for the particular aircraft and engine involved. Most operators report car-like starting as the engine fires up after as few as two turns of the crankshaft. SlickSTART, however, is not a cure-all for other engine ailments. It cannot overcome faulty priming, fuel delivery, ignition problems, or bad starting techniques. Prior to installing SlickSTART, ensure that systems related to engine starting are in good mechanical order. Operators should be advised that SlickSTART has a maximum duty time of one minute on and five minutes off.

This article has touched on some system operation and installation tips for the SlickSTART magneto starting booster. It is now being offered by several general aviation companies as a standard item including Schweizer, Grob, Diamond, and Superior. To see if the system is available for installation on your aircraft, you can contact Unison Industries to speak with a customer service professional. AMT

Harry Fenton, Unison’s manager of customer services, has worked for Unison for more than 17 years. A lifetime EAA member, Harry is an active pilot, A&P/IA, and owns several homebuilt and production aircraft. He writes the popular "Ask Harry" GA advice column published in Keep 'em Flying.

Additional ReSource

UNISON Industries

530 Blackhawk Park Avenue

Rockford, IL 61104

(815) 965-4700

(815) 965-2457 FAX